Field of the Invention
The present invention relates to a method of supplying a normally continuous operating hydraulic actuator with hydraulic fluid, continuously and by controlled pulse, and it also relates to a device for implementing said method.
Continuously operating hydraulic actuators and the system for supplying the with hydraulic fluid are well known. They are usually used for moving a load or a tool in a continuous movement over a distance which may be relatively large. Whether they work by pushing or pulling, a pressure chamber of the actuator is supplied with pressurized hyraulic fluid for moving the piston of the actuator over a part of the whole of its stroke in a continuous movement at a speed which depends on the supply pressure and on the resisting forces met by the piston rod of the actuator.
The piston rod is returned to its starting position either by means of a spring (single acting actuator) or by supplying the other chamber of the hydraulic actuator with pressurized fluid (double acting actuator).
Systems with energy accumulation are also known for supplying hydraulic fluid for hydraulic reciprocating apparatus, for example power-hammers, hydraulic picks, hydraulic rock breakers or the like, in which the piston of the actuator acts on a tool like a reciprocating hammer. In this case, the supply system always emits for each stroke of the piston, a single constant energy hydraulic pulse. Each hydraulic pulse moves the piston over the whole of its stroke. Because of their repetitive aspect, these known systems may be likened to vibrators. They can only be used on short stroke actuators (of the order of 10 cm). Since the hydraulic pulse is systematic, the effective resistance met with during movement of the piston of the actuator is in fact not taken into account and no attempt is mode to modulate the amount and value of an added hydraulic energy used as a function of the parameters of use.
In numerous technical fields, it may happen that the piston rod of a normally continuous working hydraulic actuator meets an increase in resistance in a given position of its stroke or, occasionally, in any position during its stroke. The pump and the hydraulic circuits of the supply device may of course be dimensioned so that said device is capable of supplying the actuator with sufficient hydraulic pressure to overcome such an increase in resistance. However, that results in overdimensioning the supply device with respect to the current requirements. In any case, if the increase in resistance is such that the pressure in the actuator becomes greater than the maximum pressure which the pump may provide, the actuator can no longer work.
It would therefore be advantageous to have a supply device such that a normally continuous operating actuator is capable of producing a momentary dynamic effort, in any position of its stroke, to overcome an increase in resistance during movement of its piston rod, without it being necessary to this end to overdimension the supply device.
The object of the present invention is to solve this problem.